Many types of human powered vehicles have been developed. Usually, the initial motivation is simply locomotion. Other uses which often evolve for such vehicles include physical exercise and competition, such as racing. Modern types of bicycles are generally considered to be the most efficient types of human powered land vehicles, as far as locomotion is concerned. Light alloy tubular frames, spoked wheels, and adjustable gearing contribute to a decrease in effort required to move a given distance or achieve a given speed compared to other types of human powered locomotion. In bicycle riding, the muscles of the rider's legs supply most of the propulsive effort, with the muscles of the arms and upper body providing mostly steering, support, and balance. Thus, the rider's legs receive the greatest benefits from bicycle riding efforts, along with the rider's cardio-pulmonary systems.
Another relatively efficient form of human locomotion is the rowing of boats on bodies of water. In conventional rowing, the muscles of the arms and, to some extent, the lower back provide the principal propulsive effort with the legs performing principally anchoring and balancing functions. A more efficient form of boat propelled by rowing is the racing shell in which the seat is longitudinally slidable. With the rower's feet anchored, the legs assume the principal propulsive function with the arms and back muscles providing supplementary propulsion. The legs are stronger in extension than the back is in straightening from a bend such that greater force can be applied to the oars or sculls on such vessels than on simpler rowboats. Rowing in either form provides a good workout of the arms and upper body and cardio-pulmonary exercise; and rowing of the racing shell type provides exercise to the leg muscles.
Persons without full functionality of their legs often use wheelchairs as a means of locomotion by the use of their own arms and hands, by being pushed by another, or by the operation of electric motors. Conventional occupant propellable wheelchairs generally include a wheelchair frame, large main wheels turning on an axis extending beneath the seat of the wheelchair, and small castering front wheels. The main wheels are often provided with grasping rings or push rims, approximately the same diameter as the main wheels, which are grasped by the occupant and pushed forward or pulled backward for propulsion or held for braking. Moderate self propulsion of wheelchairs by their occupants provides them with arm and upper body exercise. Sporting events involving wheelchair occupants, including wheelchair races, are often conducted to improve their morale and to induce beneficial physical exercise.
Conventional type wheelchairs, while appropriate for normal locomotion, are less than optimal for racing purposes. The need to grasp the rotating push rims in order to accelerate a moving wheelchair limits the speed of locomotion and can result in abrasions and other hand injuries. Additionally, the need to brake one wheel to steer the wheelchair results in a small decrease in speed during turns or requires than one main wheel be pushed faster than the other.
Efforts have been made to combine the propulsion mechanisms of bicycles and the physical motions of rowing to propel land vehicles. On one such vehicle, a single rear wheel has a bicycle type ratchet hub and a pair of steerable front wheels. The occupant is supported on a sliding seat similar to that on a racing shell. The front wheels are steered by differential foot movements through a linkage connected to foot platforms. A single rowing lever is engaged with the rear wheel hub through a cable and sprocket arrangement such that pulling strokes, assisted by leg extension, is converted to propulsion strokes. Such a device could, presumably, offer beneficial exercise and locomotion to a person having adequate arm and leg facility. However, a majority of persons who use wheelchairs do so because of leg dysfunction. Such persons could use a vehicle such as this only with great limitations.
There have been efforts to apply such bicycle and rowing mechanisms to wheelchairs such that the efficiencies associated with bicycle propulsion could be realized to some extent in wheelchairs by the use of the occupant's arms. The simplest forms of mechanically assisted wheelchair propulsion mechanisms include hand and arm operated reciprocating levers mounted on the wheelchair armrests which frictionally engage the tires of the main wheels. Others have included bicycle type ratchet mechanisms operated by hand levers. At least one device includes a double hand crank connected by a spocket chain to a bicycle type wheel mounted on a frame which connects to the front of a conventional wheelchair.
Most such devices involve some type of inefficiency. Many require separate right and left hand levers. Some make no provision for steering. Most involve single stroke levers such that a propulsion stroke is achieved only in one direction, such as in the pull direction, while the push stroke causes slipping of the ratchet mechanism.